1. Field Of The Invention
This invention relates to the field of heating, ventilation and air conditioning (HVAC) monitoring devices and, more particularly, to an apparatus and method for continuously monitoring the performance of a residential or light commercial HVAC systems by comparing the performance of the monitored system to the performance of an ideal industry standard system of identical size and capacity. If the performance of the system being monitored deviates from the performance of the ideal system by more than a pre-set amount, then an operator may be alerted by various means including an alarm signal sent via a modem or other signal transmission means.
2. Description of the Related Art
Actual field surveys have shown that most HVAC systems tested are operating below the manufacturer""s specifications. A small deviation from those specifications can mean a large increase in energy consumption. For example, a 10% undercharge in a system can mean the loss of almost two Seasonal Energy Efficiency Ratio (SEER) rating points, and a 23% undercharge can mean a 52% loss of efficiency.
To keep their units operating at peak efficiency, homeowners are urged by their system manufacturers and their contractors to schedule regular system maintenance. A standard maintenance call includes changing all filters, checking coolant levels and recharging, if necessary, cleaning coils and heat transfer surfaces, and making sure all air flow is unobstructed and free from dirt, foliage, etc.
There are a number of problems with regularly scheduled maintenance alone. If the coolant levels are correct, the filters are clean, and there are not other problems, the maintenance call may not have been necessary. This results in unnecessary expense and inconvenience for the homeowner. If system maintenance has just been performed, a leak may develop, or a component may malfunction shortly after the maintenance call. Unless the problem is severe enough to cause a complete system breakdown, the problem may not be noticeable to the homeowner for up to a year or until the next scheduled tune-up. This could result in ever increasing utility bills for the homeowner, and it could result in permanent damage to the HVAC system, severely shortening its life expectancy.
Performance monitors designed to address this problem use sensors to measure the difference between the HVAC system""s return (intake) air stream temperature and the supply (exhaust) air stream temperature. This temperature difference, called xe2x80x9cDelta Txe2x80x9d (D/T or xcex94T), is the best indicator of system performance. For one type of performance monitor the contractor installs the sensors in the appropriate ducts and connects the monitor to the thermostat so that it can determine whether the HVAC system is set to heat, cool, or idle. The contractor then enters the high and low heat xcex94T limits into the monitor and then the high and low cool xcex94T limits. When the HVAC system exceeds any of these xcex94T limits an alarm is sounded. These alarms can take the form of a flashing light or sounding buzzer to alert the homeowner, or a phone connection with dialer apparatus can send a recorded voice message to the contractor.
The problem with this type of monitor is that it is dependent on input from the installer to determine the proper xcex94T range. The correct xcex94T range is determined by many factors and the installer would need to have a great deal of experience to gauge the system""s potential performance correctly. This is especially true if the system is of a xe2x80x9cmix and matchxe2x80x9d variety with components from different manufacturers. Other problems occur if the components are all from the same manufacturer but of different ages, or if a new system has been installed and joined to an older, undersized or oversized duct network.
Another type of performance monitor was developed to overcome some of these obstacles. This type of monitor directly measures the xcex94T on a newly tuned or installed HVAC system that has been running for several minutes or long enough to have reached operating temperatures. This measurement is then considered the indicator of 100% performance efficiency of the HVAC system. As the performance degrades from the preset level to an unacceptable amount, e.g. 60% of ideal, then the monitor would sound an alarm.
The problem with this type of monitor is that if the HVAC system was initially installed incorrectly, the subsequent monitoring and measurements become meaningless. An additional inherent problem with the previous designs, and the main problem with existing performance monitors, is that they do not take into account the dynamic nature of the xcex94T values. The xcex94T is a number that is constantly changing over time. It is dependent not only on the temperature of the incoming air, but it is even more dependent on the relative humidity of the incoming air. If, for example, an HVAC unit, having a given CFM/Tonnage rating for cooling, has a return air temperature of 75xc2x0 F. and return air relative humidity of 25%, the operating xcex94T should be 24xc2x0 F.; however, for the same sized unit and same temperature conditions, but a return air relative humidity of 80%, the operating xcex94T drops to only 11xc2x0 F.
An additional inconvenience for the contractor or installer responding to an alert signal is not knowing what the problem could be until the HVAC unit in question or the actual performance monitor installed at the customer""s house can be examined. This can lead to delays, inconvenience, and loss if the correct parts or supplies do not arrive at the job site.
Existing performance monitors, once tripped, must all be reset manually. Even if the contractor knows the problem is temporary and will clear up on its own, someone must physically reset the monitor every time an alarm is sent. Again, this causes inconvenience for the home owner and a loss for the contractor.
Current HVAC performance monitor designs require highly skilled and experience technicians to set up the monitors. Current monitors ignore the effects of humidity of xcex94T. Currently monitors can""t compare the performance of the HVAC system they are monitoring to the system""s nominal performance as published by the manufacturer. Current monitors do not relay specific information to the contractor""s office to aid in diagnosing problems. Current monitors must be reset manually.
U.S. Pat. No. 4,611,470, issued Sep. 16, 1998 to Henrik S. Enstrom for xe2x80x9cMethod primarily for performance control at heat pumps or refrigerating installations and arrangement for carrying out the method,xe2x80x9d describes a method of primarily testing and performance controlling heat pumps, refrigerating installations or corresponding systems, in which the system performance is measured and compared to electrical energy input. This methodology has the disadvantage that it requires the electric input to be measured directly to determine if the system is running efficiently.
U.S. Pat. No. 4,432,232, issued on Feb. 21, 1984 to Vanston R. Brantley, et al. for xe2x80x9cDevice and method for measuring the coefficient of performance of a heat pump,xe2x80x9d describes a system for quick and accurate measurement of the coefficient of performance of an installed electrically powered heat pump including auxiliary resistance heaters.
Temperature sensitive resistors are placed in the return and supply air ducts to measure the temperature increase of the air across the refrigerant and resistive heating elements of the system. The voltages across the resistors are proportional to the respective duct temperatures. These voltages are applied to the inputs of a differential amplifier and a voltage-to-frequency converter is connected to the output of the amplifier to convert the voltage signal to a proportional frequency signal. An input power frequency signal is produced by a digital watt meter arranged to measure the power to the unit. A digital logic circuit ratios the temperature difference signal and the electric power input signal to produce a coefficient of performance of the system. This coefficient of performance determination method and associated apparatus have the significant deficiency that the effects of humidity, which often have enormous impact on system performance, are wholly ignored. As a result, the coefficient determined for the heating system by the method and apparatus of the Brantley et al. patent may be grossly in error, with respect to the effects of relative humidity.
It is therefore an object of the present invention to provide an efficient means and method for determining ideal operating performance levels of an HVAC unit, e.g., a residential or light commercial HVAC unit, and monitoring its performance level.
It is another object of the present invention to provide means for measuring the change in performance and telemetering monitoring data of an HVAC unit to a central computer station so that a repair and maintenance recommendation may be made for the HVAC unit.
It is yet another object of the present invention to provide a facile means of maintaining an optimum performance level of a HVAC unit in an quick, energy-efficient and economical manner.
It is a still further object of the invention to provide a means and method for monitoring and maintaining optimum performance of a thermal management system such as a HVAC unit, that overcomes the deficiencies of the prior art.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.
The present invention relates to an apparatus and method for continuously monitoring the performance of a HVAC system, e.g., a residential or light commercial HVAC system, by comparing the performance of the monitored system to the performance of an ideal industry standard system of identical size and capacity. If the performance of the system being monitored deviates from the performance of the ideal system by more than a pre-set amount, then a monitoring report can be generated and/or an operator may be alerted by various means including an alarm signal sent via a modem or other signal transmission means, and/or adjustment action can be initiated by suitable adjustment means incorporated in the system.
The present invention overcomes the problems of prior art monitoring and control systems, by directly measuring the return (intake) air relative humidity as well as the return and supply (exhaust) air temperatures. It is not necessary to measure the supply air relative humidity, because performance efficiency of standard HVAC units is not typically related to supply air relative humidity levels. The installer of the monitor needs to know only the specification of the HVAC system being installed. The installer must know the tonnage rating of the air conditioning unit and the CFM rating of the air handler to calibrate the system for cooling mode. For heat mode, the installer needs to know the CFM rating of the air handler, whether the furnace is electric or gas/fuel powered, and the size of the heater in kW or BTU capacity.
When the monitor is being calibrated, the sensor inputs are compared to optimum values for an HVAC system of the size and capacity being monitored by means of industry standard tables and equations. This comparison yields a xe2x80x9ccorrection factorxe2x80x9d which shows how close best actual system performance is to theoretical ideal system performance. If the correction factor is too large, it indicates an improper installation or faulty component which needs to be replaced.
Once the monitor has been calibrated, the sensors take readings periodically as long as the thermostat is calling for heat or cool. The monitor examines the return air temperature and humidity, calculates the xcex94T based on those readings, and offsets that xcex94T value by the correction factor. This yields the calculated xcex94T value. If the actual xcex94T varies from the calculated xcex94T by more than an established tolerance, then the monitor transmits an alarm to a central station via a suitable communication means such as for example a computer modem, facsimile, wireless transmission, direct hard-wire connection etc.
A central station downloads the telemetry data from the remote monitor and generates a complete report showing temperature and humidity data, thermostat settings, details of the problem, and details of the size, type, and capacity of the HVAC system. This report is then transmitted to the contractor responsible for the maintenance of that system giving him enough information to begin diagnosing the problem. As with the telemetry of data from the HVAC unit, the report may also be sent to the contractor via computer modem, facsimile, wireless transmission, direct hard wire connection, etc.
If the contractor needs to make repairs on the HVAC unit, he can manually reset the monitor when the repairs are completed. If the problem is something minor like a dirty filter, the contractor can simply call the homeowner to remind him to change the filter. The monitor will reset itself automatically after a programmed time, e.g., 18 hours.
These features overcome the problems inherent in previous HVAC performance monitors and enable contractors to maintain their customers"" equipment at optimum levels. This furthermore allows homeowners to save money on energy and repair bills.
Other features, aspects and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.